Imaging of Borrelia turicatae producing the green fluorescent protein reveals persistent colonization of the Ornithodoros turicata midgut and salivary glands from nymphal acquisition through transmission

Abstract

Relapsing fever (RF) spirochetes colonize and are transmitted to mammals primarily by Ornithodoros ticks, and little is known regarding the pathogen's life cycle in the vector. To further understand vector colonization and transmission of RF spirochetes, Borrelia turicatae expressing a green fluorescent protein (GFP) marker (B. turicatae-gfp) was generated. The transformants were evaluated during the tick-mammal infectious cycle, from the third nymphal instar to adult stage. B. turicatae-gfp remained viable for at least 18 months in starved fourth-stage nymphal ticks, and the studies indicated that spirochete populations persistently colonized the tick midgut and salivary glands. Our generation of B. turicatae-gfp also revealed that within the salivary glands, spirochetes are localized in the ducts and lumen of acini, and after tick feeding, the tissues remained populated with spirochetes. The B. turicatae-gfp generated in this study is an important tool to further understand and define the mechanisms of vector colonization and transmission.